The present invention relates to a device for detecting the angular acceleration of wheels, which can, when the wheels produce an angular acceleration whose absolute value is in excess of a predetermined value, accurately detect such angular acceleration without being affected by temperature conditions at the time of use, and without being affected by the finishing accuracy of parts, or by minor deviations in the shape and the material of the members used.
For example, an anti-skid brake device of a wheel may be designed so that the device may be actuated in correspondence with the angular acceleration of the wheel. In this case, however, the angular acceleration of the wheel must first be detected accurately in order to accurately actuate the anti-skid brake device.
Accordingly, the device for detecting angular acceleration of wheels in accordance with the present invention may be effectively applied to the anti-skid brake device, for example. In the present invention, the angular acceleration includes two concepts, that is, positive and negative angular accelerations, one for the positive acceleration when the wheel increases in speed in one direction, and the other for the negative acceleration when the wheel rotating in the same direction decreases in speed.
In a detecting device for detecting angular acceleration of wheels comprising a first member integrally rotating with a wheel, a second member mounted on said first member through a resilient member so that said second member may be rotated relative to said first member, and relative rotation detecting means for detecting the relative rotation between said first member and said second member, the relative rotation detecting means is generally affected by the temperature conditions at the time of use, by the finishing accuracy of the parts, or minor deviations in the shape and material of the members used. As a consequence, the relative rotation detecting means may not always operate accurately, when the magnitude of relative rotation between the first and second members reaches a predetermined value, to detect the presence of the relative rotation between the first member and the second member.
For example, one known relative rotation detecting device includes a first slit ring mounted on a first member and a second slit ring mounted on a second member, the first and second slit rings being relatively rotated with each other between a light emitting element and a light receiving element. In this device, slits in the first slit ring are normally not superposed on slits in the second slit ring and are thus maintained in a shielding state, but when the slits in the first slit ring and the slits in the second slit ring are superposed on one another to allow the light emitted by the light emitting element to pass through the light receiving element and thereby the presence of relative rotation between the first member and the second member may be detected by the action of the light receiving element on the basis of photoelectric effect thereof.
In this case, the intensity of light emitted from a light emitting element constituting the light emitting body and the light receiving sensitivity of a light receiving element constituting the light receiving body are generally influenced by the temperatures at the time of use. It therefore happens that the light receiving body is not actuated immediately when the slits in the first slit ring begin to be superposed on the slits in the second slit ring, and the light receiving body begins to be actuated for the first time when the slits in the first slit ring progress, to some extent, to be superposed on the slits in the second slit ring. Each of the slit rings is formed with a multitude of slits in circumferentially equally spaced relation. Due to the limitation of the accuracy of finishing, however, the slits in each of the slit rings are not always disposed in accurately equally spaced relation, and additionally, the circumferential widths of the slits are not always completely uniform. For this reason, even if relative rotation should occur between the first member and the second member, the transmission quantity of light differs with the particular slits superposed on one another and, as a consequence, it is sometimes difficult for the light receiving body to detect the relative rotation between the members. Further, the resilient member adapted to connect the first member to the second member unavoidably becomes somewhat uneven in shape and material depending on the product. In such a case, even if a given angular acceleration is produced in the wheel by the resilient member used, the magnitude of relative rotation produced between the first and second members may vary, and as a result, there gives rise to the disadvantage that the minimum quantity of relative rotation required for detection of the relative rotation by the relative rotation detecting device differs with different products.